With the enactment of recycling legislation and the use of bottle deposits to discourage litter, the amount of plastic film and bottles available for recycling is increasing rapidly. Ideally, scrap plastic could be recycled into new bottles or film product thereby saving landfill space, energy and raw materials. However, before the plastic is recycled it must be cleaned to remove any contaminants. Cleanliness of the plastic material to be recycled is a consideration, especially if the scrap plastic is to be recycled into beverage containers or other food-contact applications.
Many food-contact plastics, such as polyethylene and polyethylene terephthalate (PET), could be recycled as beverage containers if the cleanliness of the recycled plastic could be assured. In addition to dirt, paper, glue and other routinely encountered contaminants, some recycled plastics are contaminated from a previous application. Some liquids, such as motor oil, acetic acid and the like are sufficiently soluble in the polymer so as to diffuse into the outer layer of the plastic. Therefore it would be advantageous to remove a small amount of the recycled plastic to ensure that the contents of a previous container which may have diffused into the plastic are also removed from the recycled polymer.
In an attempt to address this problem, U.S. Pat. No. 5,073,203 discloses the use of supercritical carbon dioxide as a solvent to clean the surface of plastic flakes. While the supercritical fluid is an effective solvent, the method is expensive, and requires the use of an autoclave.
Accordingly, a need exists to provide inexpensive methods and apparatus to clean the surface of plastic so that it may be recycled.